Apparatus for liquid-gas contacting tray



Dec. 24, 1968 B. WILLIAMS ETAL 3,417,975

APPARATUS FOR LIQUID-GAS CONTACTING TRAY Original Filed Dec. 1, 1964 2Sheets-Sheet l FLOW OF LIQUID 247/ n INVENTORSY a gg BENJAMIN WILLIAMSEDWARD F. YENDALL A T TORNE Y 1968 B. WILLIAMS ETAL 3,417,975

I APPARATUS FOR LIQUID-GAS CONTACTING TRAY Original l-iled Dec. 1, 19642 Sheets-Sheet 2 I I A I m 4/5 4/4 435 INVENTORS BENJAMIN WiLLlAMSEDWARD F. YENDALL A T 'TORNE V United States Patent 3,417,975 APPARATUSFOR LIQUID-GAS CONTACTING TRAY Benjamin Williams, Grand Island, andEdward F. Yendall,

Kenmore, N.Y., assignors to Union Carbide Corporation, a corporation ofNew York Continuation of application Ser. No. 417,264, Dec. 1, 1964.This application Apr. 1, 1966, Ser. No. 547,118 12 Claims. (Cl. 261114)This is a continuation of application Ser. No. 417,264, filed Dec. 1,1964, and now abandoned, which in turn is a continuation of Ser. No.84,807, filed Jan. 25, 1961 and now abandoned.

This invention relates to an improved liquid-gas or liquid-vaporcontacting device, and more particularly, to a liquid-gas orliquid-vapor contacting tray of the type used in distillation andabsorption operations and process for its use.

In recent years, the unit operations of absorption and distillation havecome to play a major role in the chemicals industry. As more and moreemphasis is placed on these operations, the physical size ofdistillation or absorption columns, and their associated accessories,has grown accordingly. New problems heretofore unknown have arisen whenthe size of these columns is increased. A new and larger distillationcolumn for example may be installed to increase the capacity of existingfacilities only to find that unexpected inefliciencies within the columnseverely restrict its rated capacity thereby offering little or noadvantage over existing facilities. One such problem facing thedistillation art in recent years has been the decrease in trayefficiency as the size of the tray is increased to accommodate largerliquid and vapor loads.

In conventional trays and plates for liquid-gas contact columns, theliquid is induced to flow across the tray by a liquid level gradient, orhydrostatic head difference, inherently established on the tray toovercome liquid flow resistance. In small diameter trays, the liquidflow path is short and the gradient is small, and reasonably goodperformance can be obtained without special provisions to improve liquiddistribution. Such small diameter trays may be constructed in the formof level, flat perforated metal surfaces or the conventional bubble captray may be used.

In larger diameter columns, however, the liquid path is longer, liquidrate per unit tray width is greater, and a considerable ditierence inliquid depth will exist on a flat tray between the inlet and the outletweir. This greater difference in liquid depth now becomes a severeproblem in effective tray design and operation. The greater depth ofliquid near the tray inlet presents a greater resistance to vaporbubbling than the shallow depth near the outlet weir. In general,nonuniformity of bubbling results; that is, bubbling is more vigorous atthe tray outlet than at the tray inlet. In the extreme case, if thegradient is sufficiently high the tray may cease to bubble altogether atthe inlet, resulting in dumping of the liquid over this inactive region,while violent bubbling or even vapor blowing occurs at the outlet. Inany event, phase equilibrium between the liquid and the vapor will notbe obtained and the tray efficiency will be low.

The adverse effects of relying on hydrostatic gradient to promote floware particularly acute in a circular flow tray in which the liquid flowsin a circular path, perhaps 320 around a central dummy or cap.Obviously, the flow path will be much longer near the outercircumference of the tray than near the center, and yet, the samehydrostatic gradient theoretically exists for promoting flow around allpaths regardless of the radius. This means that liquid flowing near theouter circumference will proceed very slowly and may actually becomestagnant, While "ice liquid flowing near the center will traverse thetray very rapidly. This has the elfect of varying the reflux ratiodrastically between different areas on a given tray, causing a net lossin tray efficiency.

One method of eliminating liquid gradients is discussed in US. Patent2,306,367 to I. G. Benson et al. This patent teaches that by pitching orsloping the tray surface between the inlet and the over flow weir, thedifference in liquid depth may be partially or wholly eliminated.Furthermore, by the use of radial baffles on a circular flow tray, theliquid residence at all flow radii may be made uniform. While thisinnovation represents a considerable improvement over the unbafiled,flat tray, it nevertheless contains certain disadvantages which becomemore severe in larger columns and in columns where production rates varyconsiderably. Pitching the trays is quite expensive and delicate, andthe pitch which is designed into a given tray can only neutralize thehydrostatic gradient for one particular liquid load condition. Changingthe load condition on the tray causes it to be either over or underpitched. In any one rectification column, flow conditions may varyconsiderably at different levels between feed and withdrawal points, andit is clear that each level would require a special tray construction inorder to obtain optimum efiiciency corresponding to each flow condition.Furthermore, present-day columns are required to operate at varying feedand/or production rates and the pitched tray is too inflexible to bewell adapted to such rangeability. The provision of radial battles isalso expensive and their employment is rather specific for oneparticular load condition on the tray. Baflles also add more resistanceto liquid flow and therefore intensify the gradient problem.

Another method of eliminating liquid gradients from liquid inlet toliquid outlet on liquid-gas contacting trays is by means of a vapor-jettray. The apertures of the vaporjet tray are either inclined or parallelto the suface of the tray. Each aperture acts as a vapor jet originatingbeneath the surface of the liquid which causes the liquid in itsimmediate vicinity to move in the direction of the jet. By orienting theapertures in the desired direction of liquid flow, the liquid may beboosted across the tray without relying upon hydrostatic gradient.However, an important disadvantage of such trays stems from the factthat the total horizontal driving force available in all the vaporpassing through inclined apertures on such trays is usually far greaterthan that required for neutralization only of the hydrostatic gradienton the tray. A reverse hydrostatic gradient is easily encounteredwherein the liquid builds up to excessive depth near the down-comer andruns too shallow near the inlet. Thus, over-compensation introduces thesame problems as are encountered as with normal gradient in standardsieve or bubble cap trays.

The reverse hydrostatic effect in known vapor jet trays may be quiteextreme. In at least one known example, the excessive kinetic energy ofthe vapor has been utilized to deliberately cause the liquid to build upon certain selected areas of the tray. In these selected areas, theliquid depth is so great that the tray weeps, i.e. the liquid dripsthrough the vapor apertures under the excessive hydrostatic head. Theobject is to avoid having to provide a specific mechanical down-comerfor conducting the liquid to the tray below. It is apparent, however,that the extreme variation of liquid depth existing on such a trayproduces the same disadvantages met in conventional sieve and bubble captrays.

Thus, the inflexibility of known vapor-jet trays makes it extremelydiflicult to build a tray of this type which provides a satisfactorybalance between factors such as pressure drop, bubble formation, andhydrostatic gradient. A tray designed for one specific load conditionmay be entirely unsatisfactory at another condition.

An object of this invention is to provide an improved liquid-gascontacting tray which distributes the process liquid contained thereonuniformly over the surface of the tray thereby achieving maximum trayefficiency.

A further object of this invention is to provide a liquidgas contactingtray which is able to operate efficiently over a considerable range ofprocess liquid and vapor loads.

A still further object of this invention is to provide a liquid-gascontacting tray which is easily and economically fabricated andinstalled.

A still further objective is to provide liquid-vapor or liquid-gascontacting processes employing the unique tray design of this invention.

FIG. 1 is an isometric view of a portion of an exemplary tray accordingto this invention showing the relationship of one of many apertures withrespect to normal perforations extending through the tray;

FIG. 2 is a view in section taken in the direction 22 of a portion ofsuch tray with liquid thereon, illustrating an aperture profile andrepresentative tray behavior during operation;

FIG. 3 is a view in section taken in direction 33 of a portion of thecontacting tray illustrating an aperture and representative traybehavior during operation;

FIG. 4 is a perspective view of a segmental section from an actual trayof the circular flow type illustrating the variation of aperture densityfrom the center of the tray to the periphery of the tray. A qualitativerepresentation if the velocity profile acros the tray surface is shownby the increasing size of the velocity vector as the periphery of thetray is approached; and

FIG. 5, consisting of four parts, 5a, 5b, 5c, and 5d, illustratesseveral embodiments of apertures which may be employed as alternativesto the particular and preferred aperture construction illustrated anddiscussed herein.

For the purpose of orientating the viewer to the various illustrationsdepicting a flow of liquid on the gasliquid contacting tray as well asorientating the viewer to those views in which no liquid is shown on theillustrated tray of this invention, for all side views illustratedherein, the flow of liquid is or would be horizontal and perpendicularto the viewers line of sight. In all front views, the flow of liquidwill or would be directly at the viewer.

According to this invention a selected number of apertures are formed bycausing rectangular portions of a material having performationsextending therethrough, such as sieve plate material, to be raised abovethe plane of the surface of the material and one edge of the raisedsection to be completely sheared away from the material. The shape ofthe raised section resembles a lean-to having walls. The opening orfront of the raised sections thus formed produces an aperture planewhich contains the edges of the material which have been separated.Depending upon the method used to cause the raised sections to beformed, the aperture plane, containing the aperture may be caused to beinclined at some oblique angle or be normal to the plane of the tray. Aselected number of these apertures having an aperture plane inclined ornormal to the tray surface are provided on a fiat, horizontal tray so asto induce liquid flow and substantially reduce the hydrostatic gradientexisting from liquid inlet to liquid outlet. The remainder and largestportion of the free area required for vapor flow is provided I byperforations integral with and terminating at the tray surface. Theperforations integral with the tray are pr ferably in the form of smallsieve-type openings distributed uniformly over the tray surface. In thisway, only a portion of the vapor is utilized to promote liquid flow, theremainder being used to form a mass of tiny bubbles through the processliquid on the tray. By the present invention a new degree of flexibilityis introduced into tray construction which allows optimization ofpressure drop, liquid propulsion, and bubble formation. Traysconstructed in accordance with this concept exhibit low pressure dropand a uniform high degree of bubbling activity. The trays are alsocharacterized by high rangeability, the tendency to weep at relativelylow flow rates or to entrain liquid at high flow rates is reduced; thispermits a rectification column to o erate with high efficiency atproduction capacities both well above and well below the averagecapacity for which it was rated. This is an important advantage,particularly where a liquidgas contact installation serves a singleconsumer having a variable demand.

Of great advantage is the fact that one designing and distributing theapertures having aperture planes inclined or normal to the tray surfaceneed consider only the gradient problem and need not consider problemsof accommodating the total vapor flow. 'In many instances, only perhaps10% to 20% of the total open area on the tray need be provided asinclined or normal apertures; the balance being normal perforations instandard sieve material. Since the total open area is usually a smallfraction (e.g. 10%) of the total tray surface, it is clear that a totalinclined aperture area on the order of 1% to 2% of the tray surface willoften be adequate to neutralize the gradient. This means that theaperture inclined or normal planes containing the aperture will be fewin number, so that it is entirely feasible to punch the apertures in apre-determined pattern tailored to the tray geometry and expected loadconditions. It also means that apertures of relatively small dimensionmay be used which are relatively insensitive to changes in vapor flow.This rangeability of apertures, in turn permits standardizing the sizeand geometry of the apertures for a wide variety of load conditions, sothat a single shape and size of aperture will usually accommodate allusage of this invention in a given service thereby simplifying trayfabrication.

In the practice of this invention it is preferable to match the wet traypressure drops of the perforations integral with the tray and usuallynormal to the tray surface, and the aperture formed by a punchingoperation which apertures may or may not be inclined to the traysurface. This insures uniform bubbling activity on the tray and it alsoavoids weeping from either aperture or perforation. The wet traypressure drop (Ah usually measured in millimeters or inches of trayliquid, is the resistance to vapor flow through the apertures orperforation due to surface tension of the liquid, at incipient bubblingconditions, exclusive of hydrostatic head. It is readily determined bymeasuring the pressure drop across an aperture or perforation covered bya known depth of actual column liquid while maintaining only enoughvapor flow to produce bubble growth. This measurement, reduced by anyhydrostatic head included therein, is the wet plate pressure drop. Thevalue of the wet plate pressure drop depends on the size of the apertureand perforation and on the surface tension of the column liquid. Forliquid of a given surface tension, very small apertures and perforationsexhibit high values of Ah and tend toward high compression costs tooperate the column. Large apertures and perforations exhibit low valuesof Ah and tend toward weeping or dumping, especially at low vapor rates.For satisfactory performance, we have found that the formed aperturesand the perforations integral with the tray and normal to the plane ofthe tray should be sized to exhibit a value of Ah between 0.05 and 0.5inch of column liquid. Below 0.05 inch excessive weeping of the columnliquid through the tray could occur thereby decreasing tray efiiciency.Values of Ah above 0.5 inch of column liquid would increase compressioncosts thereby reducing the economy of the process. The size of theformed apertures should be chosen so that their Ah is not greatlydifferent from that of the perforations integral with the tray andnormal to the tray surface. For best performance, Ah for the formedapertures should be somewhat less than for the perforation integral withthe tray and normal to the tray surface and preferably should be between70 and 100% of the Ah for the perforations integral with the tray.

To illustrate an optimal range of size for circular perforations normalto the surface of the tray, 9. range of diameters has been establishedfor air separation. A range of 0.015 to 0.125 inch was found to operatesatisfactorily. For mechanical reasons, sheet metal cannot be thickerthan the punched hole diameter. Normal perforations having a diametersmaller than 0.015 inch will therefore necessitate the use of a traymaterial which is too thin to provide level support for the liquid. Afurther disadvantage also results if the perforation diameter is lessthan 0.015 inch, i.e., the pressure drop across the trays becomes highand power losses increase. Above a diameter of 0.125 inch normal vaporloading would be insuflicient to keep the tray from Weeping, therebyreducing tray efiiciency.

Table I presents several examples of trays having formed apertures andperforations used in air separation to illustrate the distribution oftotal Open tray area, i.e., the area given to perforations normal to thetray surface and the area given to formed apertures.

QL is the liquid flow rate across the tray expressed as cubic feet ofliquid traversing each foot width of flow path in unit time.

Hydrostatic gradient is the diiference in actual hydrostatic head whichexists across a measured length of liquid flow path. The values ofhydrostatic gradient listed in Table I were measured between points 9feet apart along the flow path. The difference in hydrostatic head alongthe tray is the difference in flow resistance encountered by vaporpassing through the tray. Therefore, a low value of the hydrostaticgradient is indicative of good distribution of vapor flow across thetray surface.

Total gas phase P is the overall loss of pressure of the vapor inpassing through the tray and liquid.

) The bubbling Index is an empirical index used during the tests toqualitatively measure the tray activity. Values of one (1) or greaterindicate a fully active tray. Values below one 1) indicate only partialtray activity. Values equal to one (1) indicate incipient bubblingconditions.

From the results listed in Table II, it is seen that by adding formedapertures, the hydrostatic gradient is greatly reduced and in some casesvirtually eliminated. The

TABLE I Formed Fraction of Superficial Reflux Perforation aperture openarea as Tray Press, vapor ratio L/V, density, density open area formedDiam., in p.s.i.g. velocity, lb. liquid, holes/sq. in. formed, (total)apertures,

tt./sec. lb. vapor apertures/ percent sq. in

It is of interest to note the wide variation in total percent open area,and that the range includes very high values of this factor.

EXAMPLE I Tests comparing the performance of this invention with astandard sieve tray were conducted for the air-water system using a trayin the form of a trough 10.5 feet long and 0.056 foot wide. The traymaterial was standard sieve material having 80 holes or perforations persquare inch and having a diameter of 0.036 inch, each perforation beingnormal to the tray surface. The same material was then used to constructthe formed aperture-sieve tray of this invention. In addition to the0.036 inch diameter perforations normal to the tray surface, a group ofapertures were formed on the surface of the tray. The formed aperturesmeasured 0.025 inch high by 0.1875 inch long. The aperture density wasfour formed apertures per square inch. The results of this traycomparison are presented in Table H.

low absolute values of the residual gradients in the formedaperture-sieve tray indicate that almost perfect fluid distribution isachieved. In spite of the fact that both liquid and vapor loadingconditions were varied drastically, by a factor of about 2, the formedaperture-sieve tray remained stable as shown by the high values of thebubbling index. On the other hand, the standard sieve tray was highlyactive only at the one condition corresponding to highest vapor velocity(4.35 ft./sec.). At intermediate vapor velocity (3.27 ft./sec.), thestandard sieve tray was at the threshold of inactivity. Finally, it isseen that the use of formed apertures reduced significantly the overallpressure drop through the tray at any given liquid and vapor load.

EXAMPLE II The results listed below in Table III were conducted in anactual air separation column under normal operating conditions. Thetrays were 52 inch diameter circular flow trays substantially identicalto FIGURE 4. The standard TABLE II.TEST RESULTS OF THE SYSTEM AIR-WATERStandard sieve tray Formed aperture-sieve tray QL/b, Hydrostatic Totaltray Bubbling Hydrostatic Total gas Vi, it.lsec. cu. ft gradient, phaseP, index gradient, phase P, Bubbling see/it mm. of mm of 111111. of mm.of activity tray liquid tray liquid tray liquid tray liquid Wherein:

V is the superficial vapor velocity and is computed as the total volumeof vapor flowing through the tray in unit time divided by the active, oropen, surface area on the tray.

sieve tray was 0.04 inch thick with 0.036 inch diameter perforationsnormal to the tray surface and distributed uniformly at a density ofperforations per square inch. The formed aperture-sieve tray, which wasmade from the same material as the standard sieve tray, had formedapertures 0.1875 inch long and 0.025 inch high. The formed aperturedensity varied from 1 per square inch near the tray center to 4 persquare inch near the periphery of the circular flow tray. As previouslydiscussed, this variation in formed aperture density was employed tocompensate for the increasing flow path which the liquid experiences asthe diameter increases. To compensate for the shorter flow path near thecenter of the tray, the liquid on the periphery of the tray must begiven a higher velocity so that the major portion of the liquid on anygiven tray will have had essentially the same residence time on thattray.

TABLE III.TEST RESULTS OF THE SYSTEM LIQUID NITROGEN-GASEOUS NITROGEN Non-slotted tray Formed aperaturesieve tray Total Total gas Total Totalgas QL/b, hydrostatic phase P, hydrostatic phase P, VI; ftJsec. on. it.,gradient, mm. of gradient, mm. of

secJtt. mm. of tray liquid mm. of tray liquid tray liquid tray liquidThe table headings are defined essentially as in Table II.

These tests of this example were conducted at a selected level in anoperating air-separation unit. A comparison of the results listed inTable III with Table II demonstrates that similar advantages overstandard trays are encountered. There is a vast improvement in the totalhydrostatic gradient which indicates that the resistance to vapor flowis essentially constant throughout the surface of the tray therebyelminating weeping and blowing.

The unique performance characteristics of this invention may betranslated into several important advances in the liquid-gas contactingart. For example, with a given size column and a given throughput, thepressure drop and hence power cost can be reduced; for a given sizecolumn and given pressure drop the productive capacity or throughput canbe increased, and; for a given throughput and given pressure drop thesize of the column can be reduced thereby substantially reducing theinitial investment.

Referring now to the drawings; the FIG. 1 embodiment of this inventionshows a portion of an exemplary tray of this invention having a mainflat surface 10. Situated on this main flat surface 10, are a number ofperforations 13 normal to the main flat surface 10 and extending throughthe tray 15. Also on the main flat surface 10 are a number of raisedsections formed from the tray having a top surface 12 inclined to themain fiat surface '10 and integral therewith. These raised sections alsohave sides 11 which are also inclined to the main fiat surface 10 andintegral therewith; the top surface 12 and the inclined sides 11 haveleading edges 12A and 11A respectively above the main flat surface 10.The flat surface just below leading edge 12A, the leading edge 12A, andthe leading edges 11A of inclined sides 11 are situated such that theyform an aperture 14 having an aperture plane which may be normal to themain flat surface 10 or slightly inclined to the main flat surface 10depending upon the manner in which the raised sections are initiallyformed.

FIGURE 2 is section (22) through FIGURE 1 showing the profile of aninclined aperture and representative tray behavior during operation. Aprocess vapor 16 rising through a liquid-gas contacting'apparatus havingliquidgas contacting trays is only allowed to flow through theperforations 13 and formed apertures 14. The portion of the vaporpassing through the perforations 13 normal to the tray surface 10proceeds through a process liquid 17 contained on the tray 15 and formsbubbles 18 while passing through the process liquid 17. In this mannerintimate contact between liquid 17 and vapor 16 is achieved. The vapor16 passing through aperture 14 does not leave the surface of the traynormal thereto as does the vapor passing through perforations 13.Instead, the vapor 16 impinges on underside surface 35 and is directedobliquely into process liquid 17. In this manner the underside surface35 acts as a gas flow directing surface. It should also be noted thatthe aperture opening 14 functions as a throat, i.e., it convertspressure drop to kinetic energy. The kinetic energy or vapor thrust 20associated with this portion of the vapor is at an angle theta (0) 21,to the tray surface 10. This inclined force vector 20 may then beresolved into its horizontal 22 and vertical 23 components. Thehorizontal component 22 is directed into and abosrbed by the processliquid 17 thereby causing the process liquid 17 to flow in the directionindicated. 24.

FIGURE 3 is section (33) through FIGURE 1 showing an inclined apertureprofile and representative tray behavior during operation. A processvapor 16 raising through a liquid-gas contacting tray 15 is only allowedto flow through the tray openings 13 and 14. The portion of the vaporpassing through the perforations 13 normal to the tray surface 10proceeds through a process liquid 17 contained on the tray 15 and formsbubbles 18. The vapor 16 passing through aperture 14 is not normal totray surface 10 as is the vapor 16 passing through perforation 13. Inthis View the flow of liquid 17 is directed at the viewer.

FIGURE 4 is a perspective view of a circular flow tray embodying theprinciples of this invention. As has been previously discussed the flowpath of a process liquid contained on the main flat surface of the traywill increase from the center 124 of the tray to the tray periphery 125.In order to allow given volumes of liquid contained on the tray 110 tohave the same residence time on the tray, the liquid near the periphery125 must be moved faster than liquid located in the vicinity of thecenter 124 of the tray. To accomplish equal residence time, the formedaperture density must be increased from the center 124 to the periphery125 of the tray. In this manner an increasingly greater amount ofkinetic energy is transferred to the liquid as one proceeds from thecenter 124 of the tray to the periphery of the tray 125. This increaseof kinetic energy imparts a greater velocity to the liquid at theperiphery than it does to liquid at the center. This increase isqualitatively shown by the increas ing size of the velocity vectors 126.

FIGURE 5, consisting of four parts, 5a, 5b, 5c, and 5d illustratesseveral formed aperture embodiments which may be used in lieu of theprfeerred formed aperture construction illustrated and discussed inpreceding FIGURES 1, 2, 3, and 4.

FIG. 5a illustrates a portion of a liquid-gas contacting tray of thisinvention having a main flat surface 210 and having first and secondapertures, 213 and 214 as well as the first aperture 213, is flush withthe main flat surface 210 but having its central axis 230 inclinedobliquely to the main tray surface 210 as opposed to the axis 231 of thefirst aperture 213 which is normal to the tray surface. In this manner,vapors passing through the second apertures 214 will have horizontal andvertical force components, 223 and 224 respectively, with respect to thetray surface 210.

FIG. 5b illustrates a portion of a liquid-gas contacting tray of thisinvention having a main flat surface 310 and having circular firstapertures 313 and tongue-like section 312 raised from the main flatsurface 310, and having open sides. The underside 335 of the tongue-likesection 312 and the main flat surface 310 forming a second aperture 314which directs a process vapor passing therethrough such that a portionof the kinetic energy possessed by the raising vapor is utilized topropel a process liquid contained on the surface 310 of the tray acrossthe tray in the direction of a liquid downcomer. The formed aperture ofthis figure (FIG. 5b) differs from the formed aperture illustrated inFIGS. 1, 2, and 3 in that the sides as 9 well as the end are at leastpartially open. Thus in FIG. 1 the inclined sides 11 are joined to flatsurface 10 so that the sides are sealed against vapor flow. The formedaperture illustrated herein (FIG. 5b) is open along the sides, as wouldoccur if three sides of the tongue were sheared from the flat materialduring the forming operation.

FIG. 5c illustrates a portion of a liquid-gas contacting tray of thisinvention having a main flat surface 410 and having a circular firstaperture 413 and having raised section 412 with pitched sides 411terminating at an apex 433. The undersides 435 of the pitched sides 411and the main flat surface 410 forming a triangular-shaped second aperture capable of directing a rising process vapor passing therethroughobliquely into a process liquid contained on the tray 415 therebypermitting a portion of the kinetic energy contained by the rising vaporto propel the process liquid across the tray in the direction of aliquid downcomer.

FIG. 5d illustrates a portion of a liquid-gas contact tray of thisinvention which employs still another type of formed aperture. The trayhas a main flat surface 510, a number of circular perforations 513 whichare normal to the tray surface 510 and a formed aperture produced by anundulated raised section having elongated depressions. The aperture 514thus formed is similar to FIG. 3 but differs in that one or moredepressions 512 are formed in the leading edge bounding the top of theaperture.

For the purpose of utilizing this invention it would be possible toinvert the formed aperture configurations illustrated herein, i.e., tocause them to extend below the surface of the tray rather than above.The function of the apertures would not be changed but their ability tofunction efiiciently would. There would be an increased hydrostatic headover each aperture which the kinetic energy, generated at the aperture,would have to overcome before being imparted to a process liquid so asto cause the liquid to flow across the tray.

Although preferred embodiments of the present invention have beendescribed and illustrated in detail, it is understood that modificationsthereto can be made all within the spirit and scope of this invention.

What is claimed is:

1. In a liquid-gas contacting tray of the sieve-type for effectingintimate contact between rising gas and liquid flowing across the trayfrom a liquid inlet to a liquid downcomer in which a member with mainflat top and bottom surfaces has a plurality of fixed size openingsuniformly distributed across such surfaces and extending therethroughwith walls perpendicular to said surfaces for gas flow, the improvementcomprising: a plurality of sections formed from said member uniformlydistributed across said surfaces, each with a top surface raised fromsaid main flat top surface, having a from leading edge separated fromsaid main flat top surface to form an elongated aperture therewith ofgreater width than height, the raised top surface being inclinedobliquely to said main flat top surface and having a back edge integralwith such surface, each section being spaced from adjacent sections bysaid main flat top surface entirely surrounding such section and eachsection being oriented with its back edge upstream of its aperture andthe aperture widths parallel to each other, the fixed size openings andapertures being sized to provide a wet plate pressure drop Ah of between0.05 and 0.5 inch liquid, the total open area of said apertures beingless than the total open area of said fixed size openings and the totalopen area of said apertures and said fixed size openings jointly formingthe entire open area through said member.

2. A liquid-gas contacting tray according to claim 1 in which eachsection is provided with two obliquely inclined side walls joining itsraised top surface with said main flat top surface as the sole supportmeans for said top surface along with said back edge.

3. A liquid-gas contacting tray adapted to be mounted transverselywithin a vertical column for effecting intimate contact between gasascending the column and liquid descending the column by flowing acrossthe tray from a liquid inlet to a liquid downcomer, said tray havingmain fiat top and bottom surfaces with a plurality of fixed sizeopenings uniformly distributed thereacross and extending through thetray with walls perpendicular to said surfaces for upward gas flowtherethrough; and a plurality of sections formed from said tray eachwith an obliquely inclined top surface raised from said main flat topsurface having a back edge integral with said main fiat top surface anda front leading edge separated from said main fiat top surface to forman elongated aperture therewith of greater width than height, with thetotal open area of said apertures and said fixed size openings jointlyforming the entire open area through said member and the aperture totalopen area comprising less than about 20% of said entire open area, eachsection being spaced from adjacent sections by said main flat topsurface entirely surrounding such section and each section beingoriented with its back edge upstream of its aperture and the aperturewidths parallel to each other directing individual jets of gastherethrough and into the liquid in the same general direction as liquidflows across the tray the fixed size openings and apertures being sizedto provide a wet plate pres sure drop Ah of between 0.05 and 0.5 inchliquid.

4. A liquid-gas contacting tray according to claim 3 in which eachsection is provided with two obliquely inclined side walls joining itsraised top surface with its main flat top surface as the sole supportmeans for said top surface along with said back edge.

5. A liquid-gas contacting tray for effecting intimate contact betweenrising gas and liquid flowing across the tray from a liquid inlet to aliquid downcomer, said tray being constructed of sieve plate materialhaving a perforated main fiat surface with circular openings of diameterbetween 0.015 and 0.125 inch extending through said sieve plate materialbeing uniformly distribtued thereacross and substantially normal to andunobstructedly communicating with said perforated main flat surface; andsaid sieve plate material having a plurality of sections formed fromsaid perforated main flat surface being entirely surrounded thereby anduniformly distributed thereacross, each section having a top surfaceraised above and integral with said perforated main flat surface with araised front edge sheared from said perforated main flat surface toprovide an aperture between said raised edge and said perforated mainfiat surface unobstructedly communicating with said said perforated mainflat surface and a back edge integral with the main flat surface, eachsection being oriented with its back edge upstream of its aperture andall aperture widths parallel to each other, the circular openings andapertures being sized to provide a wet plate pressure drop Ah of between0.05 and 0.5 inch liquid, the total open area of said apertures and saidcircular openings jointly forming the entire open area through said mainflat surface, and the aperture total open area comprising less thanabout 20% of said entire open area.

6. A liquid-gas contacting tray according to claim 5 wherein each ofsaid sections have sides raised above and integral with said perforatedmain flat surface as the sole support means for said top surface alongwith said back edge.

7. A liquid-gas contacting tray according to claim 5 wherein each ofsaid apertures is elongated such that the width of the apertures isgreater than the height of the apertures.

8. A circular flow liquid-gas contacting tray having a main flat surfacewith a plurality of fixed, uniformly sized perforations extendingtherethrough and defined by Walls substantially normal to said main flatsurface, said perforations terminating at said main flat surface and alesser number of fixed, uniformly sized apertures extendingtherethrough, each aperture being defined by walls at least the upper ofwhich is inclined obliquely to said main flat surface, said apertureshaving an increasing aperture density on said main fiat surface of saidcircular flow contacting tray from the tray center to the trayperiphery.

9. A circular flow liquid-gas contacting tray according to claim 8wherein said perforations have cross-sectional areas between about1.77X10 and 4.91 10 square inches.

10. A circular fiow liquid-gas contacting tray having a main flatsurface with a plurality of fixed, uniformly sized circular perforationsextending therethrough and defined by walls substantially normal to saidmain flat surface, said perforations terminating at said main flatsurface and a lesser number of fixed, uniformly sized aperturesextending therethrough each aperture being defined by obliquely inclinedwalls rising from said main fiat surface thereby causing each of saidapertures to extend above said main fiat surface, the leading edges ofeach of said obliquely inclined walls defining an aperture planeinclined obliquely to said main flat surface, said apertures having anincreasing aperture density on said main fiat surface of said circularfiow contacting tray from the tray center to the tray periphery.

11. A circular flow liquid-gas contacting tray according to claim 10wherein the cross-sectional area of each of said apertures issufficiently larger than the cross-sectional area of each said circularperforations so as to cause the Wet plate pressure drop of saidapertures to be between about 70-100% of the wet-plate pressure drop ofsaid circular perforations.

12. A liquid-gas contacting tray constructed of sieve plate materialhaving a main flat surface with a plurality of uniformly distributedcircular openings of diameter between 0.015 and 0.125 inch extendingthrough said sieve plate material substantially normal to andunobstructedly communicating with said main flat surface; and said sieveplate material having a plurality of raised sections formed from saidmain fiat surface each being entirely surrounded thereby and uniformlydistributed thereacross, each section having a top surface raised aboveand integral with said main fiat surface with a raised front edgesheared from said main flat surface to form an elongated aperturetherewith of greater width than height which unobstructedly communicateswith said main fiat surface with the raised top surface of each sectionbeing inclined obliquely to said main fiat surface having a back edgeintegral with such surface and each section having sides raised aboveand integral with said main flat surface as the sole support means forsaid top surface, all sections being oriented with their back edgesupstream of their apertures and with all apertures widths parallel toeach other, the circular openings and apertures being sized to provide awet plate pressure drop Ah of between 0.05 and 0.5 inch liquid, thetotal open area of said apertures and said circular openings jointlyforming the entire open area through said main fiat surface, and theaperture total open area comprising less than about 20% of said entireopen area.

References Cited UNITED STATES PATENTS 1,950,313 3/1934 Linde 2611 142,306,367 12/1942 Benson et al. 261113 2,772,080 11/ 1956 Huggins et al2611 14 2,784,953 3/1957 Ng 261114 2,853,281 9/1958 Hibshman et al261114 2,903,251 9/1959 Thrift 2611 14 3,029,070 4/1962 Koch 2611133,062,517 11/1962 Voetter et a1 261-114 3,032,478 5/1962 Bethea et al.2611 14 XR 3,095,462 6/1963 Pomper 2611 13 FOREIGN PATENTS 1,237,299 6/1960 France.

669,862 4/ 1952 Great Britain.

690,798 4/1953 Great Britain.

HARRY B. THORNTON, Primary Examiner.

TIM R. MILES, Assistant Examiner.

1. IN A LIQUID-GAS CONTACTING TRAY OF THE SIEVE-TYPE FOR EFFECTINGINTIMATE CONTACT BETWEEN RISING GAS AND LIQUID FLOWING ACROSS THE TRAYFROM A LIQUID INLET TO A LIQUID DOWNCOMER IN WHICH A MEMBER WITH MAINFLAT TOP AND BOTTOM SURFACES HAS A PLURALITY OF FIXED SIZE OPENINGSUNIFORMLY DISTRIBUTED ACROSS SUCH SURFACES AND EXTENDING THERETHROUGHWITH WALLS PERPENDICULAR TO SAID SURFACES FOR GAS FLOW, THE IMPROVEMENTCOMPRISING: A PLURALITY OF SECTIONS FORMED FROM SAID MEMBER UNIFORMLYDISTRIBUTED ACROSS SAID SURFACES, EACH WITH A TOP SURFACE RAISED FROMSAID MAIN FLAT TOP SURFACE, HAVING A FRONT LEADING EDGE SEPARATED FROMSAID MAIN FLAT TOP SURFACE TO FORM AN ELONGATED APERTURE THEREWITH OFGREATER WIDTH THAN HEIGHT, THE RAISED TOP SURFACE BEING INCLINEDOBLIQUELY TO SAID MAIN FLAT TOP SURFACE AND HAVING A BACK EDGE INTEGRALWITH SUCH SURFACE, EACH SECTION BEING SPACED FROM ADJACENT SECTIONS BYSAID MAIN FLAT TOP SURFACE ENTIRELY SURROUNDING SUCH SECTION AND EACHSECTION BEING ORIENTED WITH ITS BACK EDGE UPSTREAM OF ITS APERTURE ANDTHE APERTURE WIDTHS PARALLEL TO EACH OTHER, THE FIXED SIZE OPENINGS ANDAPERTURES BEING SIZED TO PROVIDE A WET PLATE PRESSURE DROP $HW OFBETWEEN 0.05 AND 0.5 INCH LIQUID, THE TOTAL OPEN AREA OF SAID APERTURESBEING LESS THAN THE TOTAL OPEN AREA OF SAID FIXED SIZE OPENINGS AND THETOTAL OPEN AREA OF SAID APERTURES AND SAID FIXED SIZE OPENINGS JOINTLYFORMING THE ENTIRE OPEN AREA THROUGH SAID MEMBER.